Treasurer Wayne Swan has given his strongest hint yet that the pressures driving the federal budget into a multi-billion dollar deficit will apply for the next few years.

In a speech to the Bloomberg Australia Economic Summit in Sydney, Mr Swan has spoken about troubles in the global economy "taking a sledgehammer to our budget revenues".

"The high dollar and difficult global conditions are contributing to subdued price pressures across the board, which have hit profitability," he said.

"As a result, we're seeing further hits to revenues and it's clear this will be felt right across the [forward estimates]."

The forward estimates cover the so-called budget out years up to 2016-17.

"In this budget we will prepare a new set of forecasts, as we always do, and I'll announce on the budget night," he said.

"But it is very clear that these events - high dollar, crashing commodity prices at the end of last year, the impact of profitability and prices as a whole across our economy - means that our revenues are much lower than we anticipated.

"That is impacting not just in 2012-13 but across our forward estimates."

But shadow treasurer Joe Hockey dismissed the Government's reasoning that weakening revenue was to blame for the budget's woes.

He said the Government was spending too much.

"They've obviously over-estimated revenue; they keep saying they've taken a hit to revenue, but their revenue is certainly increasing year on year," he said.

"The problem is that their expenditure is increasing as a general point as well."

Current numbers

In January, Mr Hockey promised to deliver a surplus every year of the Coalition's first term if it won office "based on the current numbers".

But, when asked today how he would manage that, he was less sure.

"We can only go off the numbers that have been published by the Government, and the numbers that have been published by the Government claim that they are going to have a surplus this current financial year," he said.

"Plainly this is not going to be the case but we are not speculating on the budget's numbers."

There have been reports in the Australian Financial Review, quoting senior government sources on federal cabinet's expenditure review committee, saying that the prospects for a surplus over the forward estimates are remote.

In December the Government dropped its commitment to deliver a budget surplus in 2012-13, citing continuing weakness in revenue.